In order to explain the background of the invention, reference will be particularly made to FIG. 1 showing a prior art device for measuring the density of salts in atmosphere. In the FIGURE, the reference numeral 1 designates a water tank which contains super pure water the resistivity of which is above 15M.OMEGA.cm. The top of the tank 1 is opened to the atmosphere. The reference numeral 3 designates a pipe for supplying the super pure water continuously to the tank 1 at a constant flow rate. The reference numeral 2 designates a valve provided at the pipe 3. The reference numeral 4 designates an exhaust pipe for exhausting the super pure water in the tank 1. The numerals 5 and 6 designate a sodium ion analyzer and a resistivity meter provided at the exhaust outlet of the exhaust pipe 4 for measuring the density of Na.sup.+ ions in the exhausted super pure water.
The device will be operated as follows:
The surface of the water in the tank 1 is in contact with the atmosphere, and the material including Na.sup.+ ions, that is, salts in the atmosphere are dissolved naturally into the super pure water. On the other hand, the super pure water in the tank 1 is exhausted to the exhaust outlet through the exhaust pipe 4 continuously at a constant flow rate. The sodium ion analyzer 5 and the resistivity meter 6 measures the density of Na.sup.+ ions in the super pure water, which density indicates the relative value of the density of salts in the atmosphere. The analyzer 5 and the meter 6 operate continuously, thereby enabling to monitor the relative value of the density continuously.
Under the prior art device of such construction, it is possible to measure the relative change of the density of salts in the atmosphere continuously. But it is impossible to measure the absolute value of the same.